The invention relates to a multicylinder internal combustion engine, especially for automobiles, with fuel-air mixture feed devices associated with two different cylinders or groups of cylinders, and an exhaust conduit system in which two catalyzers are disposed one downstream of the other, associated with the cylinder groups in such a way that the exhaust of a first group of cylinders impinges on both catalyzers, and the exhaust of a second group of cylinders is taken to the exhaust system upstream of the second catalyzer.
In a known multicylinder internal combustion engine of the type in question, one cylinder group is supplied by a carburetor with a rich fuel-air mixture and the other group of cylinders is supplied by a carburetor with a lean fuel-air mixture (U.S. Pat. No. 3,798,980). By this mixture regulation, the exhaust emission is improved, as opposed to that of an internal combustion engine in which the mixture composition is adapted to the engine's torque requirement, e.g. in such a way that the mixture composition is richer as a function of torque or power requirement (German AS No. 1,121,202), but the improvement is not sufficient to meet the requirements of anticipated legal regulations.
To improve the exhaust emission of internal combustion engines, a switching arrangement is likewise known for regulation of the air-fuel mixture delivered to the engine, by means of an oxygen measuring sensor disposed in the exhaust flow of the internal combustion engine (German OS No. 2,554,988), which produces an electric switching signal to the control device of a fuel injection system, as a function of the composition of the exhaust that results from combustion of the fuel-air mixture. In this way the fuel-air mixture can be adjusted to produce an exhaust that is as free of harmful materials as possible on a specific ratio, e.g. a stoichiometric relationship with the air index R=1. These oxygen measuring sensors have the advantage that they give a clear reliable adjustment signal in transition from a superstoichiometric to a substoichiometric composition of the exhaust at air index R=1 and vice versa. However, such oxygen measuring sensors in the hot-running phase of the internal combustion engine are without effect on the reaching of the response temperature of the catalyzers, which are also necessary here to satisfy expected legal requirements.
To prevent power losses, and to effect a saving of fuel, in multicylinder internal combustion engines with a plurality of carburetors or subdivided carburetors for feed to the cylinders by groups via separate mixture conduits, by changing fuel delivery as a function of power output of the internal combustion engine, an intermittent regulation is undertaken so that one or more groups of cylinders remain without delivery of fuel (German Pat. No. 838,518). Exhaust emission remains essentially unaffected, however, in this method for intermittent regulation in multicylinder internal combustion engines.
The present invention is concerned with solving the problem of creating an internal combustion engine of the type in question that combines the advantages of the described internal combustion engines and substantially avoids their drawbacks.
This problem is solved according to a preferred embodiment of the invention in that the fuel supply to the fuel-air mixture feed device can be switched off for the second group of cylinders, as a function of the load of the internal combustion engine. The cylinder group that can switch off is associated with the second of two catalyzers. Upstream of the first catalyzer, there is an oxygen measuring sensor, and upstream of the second catalyzer, downstream of the supply of exhaust of the second group of cylinders, there is an oxygen measuring sensor. When the second group of cylinders is switched off, it receives only air, upstream of the fuel-air mixture feed device. The exhaust pipes of the first group of cylinders are combined upstream of the oxygen measuring sensor that is upstream of the first catalyzer, to form a single exhaust pipe, and the exhaust pipes of the second group of cylinders are combined to form a single exhaust pipe, upstream of the oxygen measuring sensor that is upstream of the second catalyzer, together with the exhaust discharge pipe of the first catalyzer. In idling of the internal combustion engine, a fuel-air mixture is supplied to the first group of cylinders and the second group of cylinders receives air. It has been found to be especially advantageous that, from the idling mode up to the end of a predetermined partial load range of the internal combustion engine, the quantity of fuel-air mixture supplied to the first group of cylinders is continuosly increased, and the amount of air delivered to the second group of cylinders is increased continuously in a first part of this partial load range, and then continuously reduced to practically zero in the remaining part of the partial load range. After passing through the predetermined partial load range of the internal combustion engine, fuel-air mixture is also fed to the second group of cylinders. It has further been found to be advantageous that, after passing through the predetermined partial load range of the internal combustion engine, the amount of fuel-air mixture fed to the first group of cylinders is continuously reduced and the amount of fuel-air mixture fed to the second group of cylinders is continuously increased, until the fuel-air mixture quantities will be the same for both groups of cylinders, and the fuel-air mixture quantities for both groups of cylinders then can be increased continuously by the same amount, up to full load. After passing through the predetermined partial load range of the internal combustion engine, the continuous reduction of the amount of fuel-air mixture fed to the first group of cylinders occurs continuously, to a lesser degree than the continuous increase in the amount of fuel-air mixture fed to the second group of cylinders.
The arrangement of the two catalyzers one downstream of the other, and the separate regulation of the two groups of cylinders by their respective oxygen measuring sensors makes possible an optimal decontamination of the exhaust of both groups of cylinders, in all ranges of operation and in all operating conditions of the internal combustion engine, with retention of the advantages of fuel saving and prevention of power losses. If the internal combustion engine works with only the first group of cylinders, then all exhaust components in the exhaust of this group of cylinders are partly decontaminated by simultaneous oxidation and reduction in the first catalyzer. The second group of cylinders in this operational state of the engine works as an air pump because of the air that is fed to this group of cylinders, so that this air is fed to the exhaust of first group of cylinders upstream of the second catalyzer, and thus there is a supplementary oxidation of the exhaust from the first group of cylinders in the second catalyzer. In this way the carbon monoxide and hydrocarbons in this exhaust are still further reduced. At the same time the oxygen measuring sensor and the catalyzer of the second group of cylinders are preheated by the exhaust of the first cylinder group, in case they have not yet reached their operational temperature, so that when the second group of cylinders is switched in, its exhaust decontaminating system is immediately ready to function.
If both groups of cylinders are working, the mixture of exhaust gases from the first and second groups of cylinders is measured by the oxygen measuring sensor upstream of the second catalyzer, and the composition of the fuel-air mixture for the second group of cylinders is so controlled that the exhaust composition at the oxygen measuring sensor upstream of the second catalyzer will correspond to a fuel-air mixture composition for the two groups of cylinders with an air index of R=1. Thus, defects in the fuel-air mixture composition for the first group of cylinders would be taken into account by the composition of the fuel-air mixture of the second group of cylinders. In this operational state of the internal combustion engine, there is moreover oxidation and reduction of the exhaust from the first cylinder group, as well as of that of the second group.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiment in accordance with the present invention.